First observed redds give hope to success of remedial actions in Laurinvirta, the River Pielisjoki
Landlocked Atlantic salmon and brown trout reproduce in running waters. Natural habitats of landlocked salmon for reproducing have almost disappeared in Finland because of river damming.
Ministry of Agriculture and Forestry, local electricity company, and other companies and private organizations funded the restoration and watering of an old dammed river channel, Laurinvirta, at the Kuurna Rapids, the River Pielisjoki. Laurinvirta is one of the top targets in the government’s policy of recovery actions for migratory fish. Laurinvirta is open in its downstream end, and fish have a free entrance there from Pielisjoki and the downstream lakes.
The field group consisting of researchers and assistants from Natural Resources Institute Finland (Luke), Ģֱ, and co-operative Vesi-Visio surveyed the redds of landlocked salmon and trout in Laurinvirta and the Joensuu Rapids 10 to 12 December 2020.
Fiver redds with eggs were found in Laurinvirta, but the area surveyed was one fourth or less of the area suitable for spawning. This was because of high discharge during the field days.
The flow in Pielisjoki was 50 % higher than the median of the season in previous decades. Spillwater had to be released through the floodgates to Laurinvirta, thus the discharge was 145 m3/s.
“The power company Laurinvirta Oy could reduce the flow down to half of that for some hours, which helped considerably the redd counting. Yet, the flow was high for wading, but the scuba diver of Vesi-Visio could enter deeper areas”, says one of the coordinators, researcher Jukka Syrjänen, Department of Biological and Environmental Science, Ģֱ.
In Natural Resources Institute Finland, senior researcher Matti Janhunen coordinates the investigation.
Fish species in redds are identified next spring and autumn
Despite of restricted sampling effort, waders found two redds and the diver found three redds. All five are situated in artificial gravel beds just upstream from the constructed spawning sill.
The researchers find the results promising.
“Very probably, there are more redds in the channel. We are going estimate the number of summerling parr by electrofishing this autumn. After a year or two we know more about the suitability of Laurinvirta to landlocked salmon”, ponders Janhunen.
The group spotted two redds in the western channel of the Joensuu Rapids as well. Again, wading was possible only in narrow shreds close to river banks due to high flow.
The redds were marked with painted marker stones and bobbers. Some hatched alevins are sampled next spring, if the flow is not too high, and taken to DNA analysis to identify the species, i.e. salmon or trout. Redds, eggs, and alevins of both species are similar and impossible to identify by their appearance.
Second picture: Diggings were verified as redds by observing some eggs. The eggs were returned to the bottom gravel. Credit: Ģֱ/Jukka Syrjänen
Field work was mainly funded by the compulsory fees of the hydroelectric power stations and industry on the River Pielisjoki. In addition, R. Erik and Bror Serlachius Foundation, and the Foundation of Raija and Ossi Tuuliainen fund the project in Ģֱ. The project is part of the project . Daiwa Sports Ltd donated the hand nets used in observing eggs.
More information:
Jukka Syrjänen, Ģֱ, jukka.t.syrjanen@jyu.fi
Matti Janhunen, Natural Resources Institute Finland, matti.janhunen@luke.fi
The Faculty of Mathematics and Science
Communications Specialist Tanja Heikkinen, tanja.s.heikkinen@jyu.fi, +358 50 472 1162
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